Radiative properties of water clouds: simple approximations

A polynomial approximation for Mie scattering characteristics is applied in the long and shortwave regions. Expressions for the absorption, scattering and extinction coefficients, single scattering albedo and asymmetry factor are obtained. The integration over the droplet size distribution is done analytically and the resulting expressions are found to be sufficiently accurate (within 3% for the tenth order polynomial approximation in the IR region) and computationally fast. When only the first two terms are kept in the polynomial expansions, the resulting expressions reduce to the Slingo parameterization of the radiative properties of clouds in the shortwave region. It is shown that this parameterization is more accurate than approximations based on geometrical optics and anomalous diffraction theory.